On Fri, Jan 4, 2019 at 3:15 PM Brent Meeker <[email protected]> wrote:
> > *You said t was the proper time for me to take the trip. * > Yes. > > *But the proper time is what a clock measures * > Yes, > > *and so it depends on the path you took in making the trip. * > Yes. And that is exactly why proper time is *NOT* an invariant, but the 4D length through spacetime is. >> I said "proper time is *NOT* an invariant"! > > > * > You apparently use "invariant" in a strange way. * > I only know how to use the word one way, a invariant is something that doesn't change with a change in coordinates. *>Proper time is an invariant length of a path in 4-space. * > No No a thousand times NO!! Proper time is not the length of ANYTHING in 4-space and proper time is NOT a invariant, Newton thought it was but Einstein showed it was not. > > *Invariant means that all different observers agree on it. * > And I and my astronaut twin do not agree on the proper time, if we did we'd still be the same age when he returned to Earth and we're not. > > *It doesn't mean the length of a path is independent of the path.* > It does mean the 4D length between events is independent of the path. > >>No observer agrees on that because no observer knows what the hell >> meters minus seconds means. But you did agree above that proper time is the >> time measured by a clock along any line through spacetime, so for my twin >> that was on a rocket at near light speed and then returned the proper time >> is one year, but for me who stayed on Earth the proper time was 10 years. >> Therefore proper time can not be a invariant, therefore the length of the >> path through spacetime can NOT be the proper time because the length of >> the path through spacetime IS an invariant. > > *> The length of which path? * > The length of any 4D spacetime path between Event A and Event B that you care to name. The distance between events is always the same regardless of the particular path chosen, the distance traveled in the X,Y and Z directions could all be different, and t could be different too, but when anybody calculates X^2+y^2 + Z^2 - (ct)^2 they always get the exact same number because the spacetime distance is an invariant. > > *Every observer can read the clock as it moves along the path and they > will all agree on the length of the path. * > They all agree on the length of the 4D path through spacetime to get from Event A to Event B but if they took different paths they will disagree on the distance traveled through space and the time it took to make it aka the proper time. > >> They don't agree on the spacial interval or the time interval, but > they agree on the proper time the clock measures along the path. THAT's > what "invariant" means. > > > *You are using the word "observer" as though it referred to a traveler, > but in relativity it usually means someone measuring a physical process > from a different state of motion. * > If I'm measuring a clock that is in a different state of motion, that is to say a clock that is not in my reference frame, then what I am measuring is NOT my proper time. > >>Proper Time is defined as the amount of change an observer has seen a >> clock make that is in the same reference frame as the observer. >>> >>> > > * > NO. The definition doesn't require the observer to be moving with the > clock. * > At this point you're not even trying, if I say X=Y all you can say is "no, X is not y". An argument is not just contradiction <https://www.youtube.com/watch?v=uLlv_aZjHXc> John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
